Lubricating oils used in passenger cars and heavy duty diesel engines have changed over the years. Today's engines are designed to run hotter and harder than in the past. However, an adverse affect of running hotter is that oxidation of the oils increases as the operating temperature of the oil increases. Oxidation of the oils may lead to a viscosity increase in the oil and the formation of high temperature deposits caused by agglomerated oxidation by-products baking onto lubricated surfaces. Accordingly, certain phosphorus and sulfur additives have been used to reduce engine oil oxidation.
However, the next generation of passenger car motor oil and heavy duty diesel engine oil categories may require the presence of lower levels of phosphorus and sulfur containing antioxidant additives in the formulations in order to reduce contamination of more stringent pollution control devices. It is well known that sulfur and phosphorus containing additives may poison or otherwise reduce the effectiveness of pollution control devices.
With regard to the above, a need exists for a lubricating additive that provides excellent antioxidant properties and is more compatible with pollution control devices used for automotive and diesel engines. Such additives may contain phosphorus and sulfur or may be substantially devoid of phosphorus and sulfur.
In one embodiment herein is presented a lubricant composition comprising a base oil, a hydrocarbon soluble molybdenum compound, and an antioxidant effective amount of one or more polymeric compounds devoid of ester linkages of the formula:
wherein R and R1 are independently selected from C1 to C12 hydrocarbyl groups; n is an integer ranging from about 0 to about 10; and A is a hydrocarbyl group having from about 1 to about 30 carbon atoms.
In another embodiment, there is provided an additive concentrate for a lubricant composition. The concentrate includes an organomolybdenum friction modifier and an antioxidant effective amount of one or more polymeric compounds devoid of ester linkages of the formula:
wherein R and R1 are independently selected from C1 to C12 hydrocarbyl groups; n is an integer ranging from about 0 to about 10; and A is a hydrocarbyl group having from about 1 to about 30 carbon atoms and is selected from the group consisting of:
wherein R2 is selected from the group consisting of C1 to C4 alkyl groups.
A further embodiment of the disclosure provides a method of reducing oxidation of engine lubricant compositions during operation of an engine containing the lubricant composition. The method includes contacting one or more engine parts with a lubricant composition comprising an oil of lubricating viscosity, an organomolybdenum friction modifier, and an antioxidant effective amount of one or more polymeric compounds devoid of ester linkages of the formula:
wherein R and R1 are independently selected from C1 to C12 hydrocarbyl groups; n is an integer ranging from about 0 to about 10; and A is a hydrocarbyl group having from about 1 to about 30 carbon atoms and is selected from the group consisting of:
wherein R2 is selected from the group consisting of C1 to C4 alkyl groups. The method further includes operating the engine containing the composition.
As set forth briefly above, embodiments of the disclosure provide an antioxidant additive composition that may significantly improve the oxidative stability of a lubricant composition and may enable a decrease in the amount of phosphorus and sulfur additives required for equivalent oxidative stability. The additive may be mixed with an oleaginous fluid that is applied to a surface between moving parts. In other applications, the additive may be provided in a fully formulated lubricant composition. The additive is particularly directed to meeting the current GF-4 and proposed GF-5 standards for passenger car motor oils and PC11 standards for heavy duty diesel engine oil as well as future passenger car and diesel engine oil specifications.
The compositions and methods described herein are particularly suitable for reducing contamination of pollution control devices on motor vehicles or, in the alternative, the compositions are suitable for improving the oxidative stability of lubricant formulations. Other features and advantages of the compositions and methods described herein may be evident by reference to the following detailed description which is intended to exemplify aspects of the preferred embodiments without intending to limit the embodiments described herein.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the embodiments disclosed and claimed.